Catalog Information
- INTRODUCTION
- MERGED DATA SETS
- ASTROMETRIC DATA: currently recommended
- ASTROMETRIC DATA: superseded or not recommended
- INFRARED SOURCES
- CATALOGS FORTHCOMING
- DOUBLE STAR CATALOGS
- MAGNITUDES AND SPECTRAL TYPES
- PARALLAXES
- VARIABLE STARS
I. INTRODUCTION
The following is a list of widely used or well known catalogs for astronomical data. It is intended to give users some basic information with regards to the content and usefulness of each. It is not intended as a substitute for journal articles nor the catalog introductions. Within each section the catalogs are listed with progressively more and fainter stars but generally with decreasing accuracy. Note that all astrometric observations and measurements should now be made in the International Celestial Reference System (ICRS), represented by the Hipparcos Catalog Reference System (HCRS), which is consistend with the older "J2000" equinox system. Astrometric data in all recommended catalogs listed here give positions and motions on the HCRS.
II. MERGED DATA SETS
The following 2 sets contain merged data, combined from several individual catalgs. These are highly recommended for users not familiar with details of various catalogs. The merged data sets are provided as a simple one-stop-shopping convenience for many customers.
Naval Observatory Merged Astrometric Dataset:
Status: Recommended for use
When compiling a star list, if astrometry is important
then there are a few data sources that one should use.
Using an obsolete source catalog could add a
factor of 100 to the positional error. As a rule of
thumb, the US Naval Observatory typically recommends
the following order of priority given for compiling star
lists from various catalogs:
1) Hipparcos Catalogue, else
2) UCAC2 catalog (for stars of about magnitude 10 or fainter), else
3) Tycho-2 Catalogue, else
4) USNO-B catalog
Although often necessary, merging differing data sets can be an enormous job that many are not willing to undertake. Over the last year, the USNO has worked on merging the above mentioned data sets (including a few others) into a large dataset. This dataset, termed NOMAD, is accessible on-line through the USNO image and catalog archive server. It is designed to be easy to use and will provide the best astrometry (and often the best photometry) for any set of stars. However, NOMAD is not a compiled catalog. If a star is listed in several catalogs only 1 catalog entry is choosen for any item. For this first release NOMAD does not contain positions or proper motions averaged over several catalogs. Different catalogs have different systematic errors and no attempt has been made here to mitigate systematic differences between original catalog data. For details, the NOMAD readme file and info on individual source catalogs need to be consulted.
Some of NOMAD's characteristics include:
- NOMAD contains over 1 billion stars
- All bright stars are included
- Faint limiting magnitude is the USNO B1 (about V=20)
- Position and proper motion listed for each star
- Best astrometry, regardless of source catalog
- Systematic errors inherited from source catalog
- Source catalog is identified
- Cross references to catalogs are given
- Several photometric bands, including 2MASS near IR
- User defined parameters
- Graphical User/Web Interface at this USNO site
- Stand alone workstation for DoD applications can be
requisitioned from USNO.
WCCD (Washington comprehensive catalog database):
Status: Internal to USNO
Most of the data for bright stars discussed below have been combined in
the Washington Comprehensive Catalog Database. For each of the 2.5 million
stars in the database, the best available data on position, proper motion,
parallax, magnitude, variability, spectral type, and multiple components
are given.
Work is underway to provide fluxes at standard photometric bands.
This may require making new observations when the data
for certain stars are found to be inadequate for a particular
requirement. The catalog will evolve continuously as new results from
observational programs are received, thus ensuring that the WCC will
contain the best possible values for each of the parameters at any
given time. The stars are extensively cross-referenced.
Data from this database are made available through requests made
to the USNO.
The WCC contains more information per star than the NOMAD (see above)
else is mostly superseded by NOMAD.
III. ASTROMETRIC DATA: recommended
The following is a list of recommended, individual catalogs for astrometric applications.
Hipparcos:
Status: Recommended for use
This catalog contains 118,218 stars that were observed by the
European Space Agency's Hipparcos Satellite, operational from late 1989
to 1993. It is complete to V=7.3. The positional accuracies of
1 to 3 mas at epoch 1991.25 are unsurpassed in the optical.
Proper motion accuracies, of around 1 to 2 mas/yr, remain state of the
art. Thus typical positional errors at a 2005 epoch are around 15 mas.
By international agreement, the Hipparcos catalog is the standard
reference catalog for optical astrometry, representing the ICRF in the
optical wavelengths. However, in 1999 this agreement was amended
to exclude approximately 18,000 stars having flags in column 59,
the so-called ``problem'' and double stars. Hipparcos also contains
broad band visual photometric data including variability information.
For the brighter stars, this is in the
1 to 2 millimagnitude range. Two color photometry from the Tycho experiment
(also flown on the Hipparcos satellite) is also published and is estimated
to be good to better than 0.1 magnitudes. The catalog is extensively
documented. The Hipparcos Catalog Data is purely based on observations
performed in space, except for the global orientation of its refrence
frame which was adjusted to the existing system by a variety of
mainly ground-based techniques.
Tycho-2 Catalog:
Status: Recommended for use
This catalog is the result of a joint collaboration between (primarily) the
Copenhagen University Observatory (CUO) and the USNO. CUO re-analyzed the
Tycho data from the Hipparcos satellite, which led to better positions
for the Tycho-1 stars, as well as extending the number of stars from
1 million to 2.5 million. The USNO was responsible for computing the
proper motions, which was done by combining over 140 astrometric
catalogs. The result is a global reference catalog that is 99% complete
to V=11.0 and 95% complete at V=11.5. Positional accuracies range from
about 10 to 100 mas, depending on magnitude. Proper motion accuracies
are from 1 to 3 mas. Two color photometry from the Tycho experiment is
published, as well. This catalog, along with documentation, is available
by contacting the USNO (nz@usno.navy.mil).
The Tycho-2 Catalogue is based on a mix of 1991 space-based data
combined with early epoch ground-based astrometry.
UCAC2 (USNO CCD Astrograph Catalog, 2nd release):
Status: Recommended for use
Caveats: Northern 15% of sky not yet available
The UCAC2 is a preliminary catalog of stars covering 86% of the sky,
from the South Celestial Pole to a ragged Northern boundary between about
+40 and +50 degrees declination. It has 48 million stars which are
primarily in the in the R=8.0 to 16.0 magnitude range. Positions are
based on recent observations taken at Cerro Tololo, Chile and Flagstaff, Arizona,
using the USNO 8-inch astrograph. Proper motions for stars brighter than
about 12.5 were derived in the same way as for the Tycho-2 stars including
Hipparcos and Tycho data. Fainter stars utilized the positions in the
"Yellow Sky" catalog, based on measures of the Lick Northern Proper Motion
(NPM) and Yale/San Juan Southern Proper Motion (SPM) plates.
Positional accuracies are 20 to 70 mas, dependent
primarily on magnitude. Proper motion errors are 1 to 7 mas/yr, also
magnitude dependent. UCAC2 is about 85% complete in the area covered.
All "problem" stars, like blended images or extended galaxies
were excluded from this release.
Observed photometry is one color and should be used for
identification purposes only; however, 2MASS near IR photometry and
cross reference information are included. This catalog is available
by contacting USNO, see also
here..
UCAC2 Bright Star Supplement:
Status: Recommended for use
Caveats: Should only be used with UCAC2.
The UCAC2 Bright Star Supplement, UCAC2 BSS, is meant to be used with the
Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2) to
fill in the missing bright stars and not-yet published northern
regions of the UCAC2. In total 430,000 stars, mostly from the region
north of +40 degrees declination, make up this supplementary data
set. All stars were extracted from either the Hipparcos Catalogue
or Tycho-2 Catalogue. 2MASS photometry and cross-reference data are
included.
The BSS is available here.
USNO B1.0 Catalog:
Status: Recommended for use
USNO-B1.0 is an expansion of the USNO-A catalog series. The major differences
are the number of stars and the inclusion of proper motions. The USNO-B1.0
contains entries for 1,042,618,261 stars/galaxies
which were detected in the digitized images of several photographic
sky surveys. The size of the entire catalog is over 80 Gbytes, and there is
no plan to distribute the entire catalog by network download; moderate sized areas can be downloaded over the internet using the USNO image and catalog archive server.
B1.0 presents right ascension and declination, proper motion, magnitude estimates and associated error terms. It is estimated that the positional error
at current epoch is near 200 mas.
IV. ASTROMETRIC DATA: superseded or not recommended
The following is a list of widely used or well known catalogs which now are outdated for most applications.
FK5 Part I (Fifth Fundamental Catalog - The Basic Fundamental
Stars):
Status: Effectively replaced by Hipparcos
This catalog contains the same 1,535 stars as its predecessor, the
FK4, but with improved zero points, more internal consistency and
smaller individual errors in the stars' positions and motions. This
part of the FK5 defined the FK5, J2000.0 system. The
average density, however, is only one star per 27 square degrees. The
errors quoted in the catalog indicate that on the average the errors
at 2000 should be near 0.05 second of arc; however, current observations
indicate that the errors may be as great as 0.10 second of arc,
especially in the Southern Hemisphere. Results also show that
there are systematic errors of 0.10 and more in parts of the sky,
especially south of -50 degrees.
FK5 Part II (Fifth Fundamental Catalog - The FK5 Extension):
Status: Effectively replaced by Hipparcos
This part of the FK5 was created for two reasons: First, in addition to
the low density, Part I does not have a uniform distribution of stars.
Second, the average magnitude in Part I is 4.8 and there are very few
stars fainter than 6th magnitude. The USNO collaborated with the
Astronomisches Rechen-Institut (Heidelberg) to produce this catalog of
3,117 stars. Thus, the complete FK5 catalog has an average density of
one star every 8.9 degrees. Great care was taken to ensure an even
distribution over the sky and in both magnitude (to 9th) and spectral
type. The positions and motions were compiled differentially on FK4
and transformed to the FK5, J2000.0 system. These stars represent the
FK5 system sufficiently well to be part of the FK5 catalog. They have
an average accuracy of 0.15 second of arc at 2000.
IRS (International Reference Stars):
Status: Effectively replaced by Hipparcos
The IRS comprises a whole-sky catalog that, by international agreement,
was the standard reference for reductions over limited areas. (Currently,
the internationally agreed standard reference is the Hipparcos Catalog).
The list was formed by combining the AGK3R in the north with the SRS in
the south. The catalog was compiled at the USNO by combining 124 meridian
circle catalogs and resulted in positions accurate to 0.22 second of arc for
36,027 stars (about one star every 1.1 square degrees), mostly in the 7th to
9th magnitude range. This extends the FK5 system to a much higher
density. The positions and motions of 2,100 of the FK5 Extension
stars come directly from the IRS. The catalog is available referred
to both FK5, J2000.0 and to FK4, B1950.0.
ACRS (Astrographic Catalogue Reference Stars):
Status: Effectively replaced by Tycho-2
For some time there has been a general need for a replacement to the
Smithsonian Astrophysical Observatory Star Catalog (SAOC), and therefore the
USNO compiled the Astrographic Catalog Reference Stars. This work was
completed in 1991 and incorporated all suitable star catalogs available at the
time. Some 1,700,000 star positions from 170 meridian circle and
photographic catalogs were combined to produce 320,211 positions and
proper motions. This gives an average density of 7.9 stars per square
degree down to magnitude 10.5, and the average positional error is
0.23 second of arc at 2000. Like the IRS, the positions and motions
are referred to both FK4, B1950 and to FK5, J2000.0.
The observational histories of some of the stars are not as good as
others. Part I contains the stars with the better histories and
generally more accurate positions and motions. Part II consists of
stars with proper motions derived from only two positions
or with high mean errors.
PPM (Catalog of Positions and Proper Motions):
Status: Effectively replaced by Tycho-2
The PPM catalog was compiled at
the Astronomisches Rechen Institut in Germany and contains
approximately the same stars as the ACRS north of -2.5 degrees, but
more south of there due to the inclusion of a recent southern
observing program. The catalog has 181,731 stars (8.6 per square
degree) in the northern portion and 197,179 (9.7 per square degree) in
the southern, for an overall density of 9.2 stars per square degree.
The positions and proper motions are given for FK5, J2000.0 only. The
northern and southern parts of the PPM were compiled separately and,
thus, there may be a discontinuity at the -2.5 degree line. The
formal errors quoted in the catalog give an estimated accuracy of 0.30
second of arc at 2000 for the northern half and 0.16 second of arc for
the southern. Since both the ACRS and the PPM are based on the IRS,
it is recommended that, for now, the ACRS be used north of -2 degrees
and that the PPM be used south of there.
Tycho-1 Catalog:
Status: Effectively replaced by Tycho-2
Caveats: Very poor proper motions
This one million star catalog contains positional and photometric
data from the ``star mapper'' flown on the Hipparcos satellite. The
positional accuracies are 30 to 50 mas at mean epoch of 1991.25. However, the
proper motion errors are quite large, at 20-30 mas/yr, making conversions
to other epochs not recommended. The ACT reference catalog, compiled using
positions from Tycho-1 and the Astrographic Catalogue (see description below),
improved the proper motions ten-fold. Tycho-1 also contains two-color
photometry (blue and visual) for most of its stars.
ACT Reference Catalog:
Status: Effectively replaced by Tycho-2
The ACT Reference Catalog was compiled at USNO for the express goal of
improving the Tycho-1 proper motions. (Note that this is very similar to the
Tycho Reference Catalogue, described below). To do this, data from the
century-old Astrographic Catalogue was combined with the Tycho-1 positions
to determine proper motions for 988,758 stars with about a 100 year base-line.
Reductions of the Astrographic Catalogue data were made at USNO,
independently of those used in the TRC. Photometry from Tycho-1 is
included, as are cross-references with Tycho-1 and Hipparcos.
Tycho Reference Catalogue, TRC:
Status: Effectively replaced by Tycho-2
The Tycho Reference Catalogue, TRC, was compiled to improve the proper motions
of the Tycho-1 catalog. (Note that this is very similar to the ACT Reference
Catalog, described above). TRC contains 990,182 stars
whose proper motions are the result of combining the Tycho observations
with those found in the Astrographic Catalogue. Reductions of the
Astrographic Catalogue data were made in the former Soviet Union,
independently of those used in the ACT Reference Catalog. Photometry from
Tycho-1 is included, as are cross-references with Tycho-1, Hipparcos
and the Henry Draper Catalog.
AC 2000.2 (The Astrographic Catalogue):
Status: Limited usefulness by itself due to early epoch
Caveats: Positional catalog only, no proper motions
The Astrographic Catalogue (AC) was an
international program to photograph the entire sky and obtain positional
measures on all stars 11.0 magnitude and brighter (although there are
many stars in the AC as faint as 13.0). The average plate epoch is around
1905, with some observed as early as 1891 and a few as late as 1950.
Two reductions have been made, forming AC 2000 and AC 2000.2. The latter
is now recommended for use.
The positions derived from the AC have been combined with modern observations
to compute proper motions. Specifically they have been combined with
Tycho-1 to form the ACT Reference Catalog, Tycho-2 positions to form the
Tycho-2 proper motions, and UCAC to form much of the UCAC1 and UCAC2 catalogs.
UCAC1 Catalog (USNO CCD Astrograph Catalog, 1st release):
Status: Superseded by UCAC2
Caveats: Contains most of S. Hemisphere, none of the N. Hemisphere
The UCAC1 is a preliminary catalog containing 27 million stars in most of the
Southern Hemisphere in the R=8.0 to 16.0 magnitude range. Positions are
based on recent observations taken at Cerro Tololo, Chile using the
USNO 8-inch astrograph. Proper motions for stars brighter than about
12.5 were derived in the same way as
the Tycho-2 were. Fainter stars utilized the positions in the USNO A2.0
for proper motion determination. Positional accuracies are 20 to 70 mas,
dependent
primarily on magnitude. Proper motion errors are 1 to 12 mas/yr, also
magnitude dependent. Photometry is one color and should be used for
identification purposes only.
GSC 2.2 (Guide Star Catalog version 2.2):
Status: Not recommended for use, use NOMAD, Tycho-2, UCAC2 or USNO B1.0
Caveats: No proper motions
The Hubble Guide Star Catalog version 2.2 is an expanded version of
GSC 1.2 with many of the problems in the latter corrected. It contains
positions and one color
photometry for 435 million stars down to ~19th magnitude.
Currently no proper motions exist, but
there are plans to include them if resources permit. It is based on plate
measures made at Space Telescope Science Institute in Baltimore.
Positional errors at the plate epoch are estimated to be in the
200-250 mas range.
Due to its similarity in magnitude range with USNO-B, but having half as many stars and no proper motions, it is reccomended that USNO-B be used instead.
GSC 1.2 (Guide Star Catalog version 1.2):
Status: Effectively superseded by GSC 2.2 and USNO-B1.0
Caveats: No proper motions
The Hubble Guide Star Catalog version 1.2 contains positions for 19 million
stars down to 16th magnitude, although it is not complete to this level.
No proper motions exist. It is based on plate measures made at
Space Telescope Science Institute in Baltimore. Positional errors at
the plate epoch are estimated to be near 500 mas.
USNO A2.0 Catalog:
Status: Superseded by USNO B1.0
Caveats: No proper motions
USNO-A2.0 contains entries for 526,230,881 stars
which were detected in
the digitized images of three photographic sky surveys.
For the entire northern sky and the southern sky down
to declinations of -30deg., all the photographic plates were part of the
original Palomar Optical Sky Survey
(POSS-I). Photographs were taken on blue- and red-sensitive emulsions.
Only those stars which were
detected in both colors were included in the USNO-A2.0 catalog.
The rest of the southern sky was covered by
the Science Research Council (SRC)-J survey and the European Southern
Observatory (ESO)-R survey.
Again, only stars appearing in both colors were accepted for the final
catalogue. USNO-A2.0 is contained on
10 CD-ROMs.
A2.0 presents right ascension and declination (J2000, epoch of the mean of
the blue and red plate) and the blue and red magnitude for each star.
It is estimated that the positional error at plate epoch is near 250 mas.
Note that no proper motions are given.
USNO Select A2.0 Catalog:
Status: Outdated, no longer available, use subset of NOMAD or UCAC2
Caveats: No proper motions
USNO-SA2.0 is a subset of USNO-A2.0 which is a lot easier to handle on
a small computer because it
contains only a tenth as many stars as the parent catalog
(54,787,624 stars in all). The goal in creating this
smaller catalog was to provide a spatially uniform distribution of
stars in an intermediate range of magnitudes
which would be useful as a ``reference grid'' for astrometric analysis.
V. INFRARED SOURCES
CPIRSS (Catalog of Positions for Infrared Stellar Sources:
Status: Recommended for use, but 2MASS should be used for data in the
near IR
The CPIRSS is the result of combining NASA's Infrared Astronomy Satellite
Point Source Catalog (IRAS) with the data of the catalogs in Section I.
The description of the original CPIRSS, released January 1994,
can be found in the Astronomical Journal 107 1 pg 280-286. Two upgrades
have been made since the original release. In 1996, 4022 new sources were
added, bringing the total to 37,700. In 2000, better astrometry was
substituted. Of the 37,700 stars, all but 105 were found in either the
Hipparcos or Tycho-2 catalogs. The astrometry for these are given,
as well as the observed IRAS fluxes at 12, 25, 60 and 100 microns. Computed
fluxes at 2.2 microns are given for the 18,000 stars that show no evidence of
excess emission in the infrared; however, 2MASS provides better 2.2 micron
photometry.
2MASS Catalog (Two-Micron All Sky Survey):
Status: Recommended for use
Caveats: No proper motions
The 2MASS project released data from the entire sky in March 2003. Data
fall primarily into 2 categories, point sources and extended sources.
The point source catalog contains 470 million objects, mostly stars.
the extended source catalog contains data on 1.6 million objects.
Observations are in three photometric bands in the near infrared;
J (1.25 microns), H (1.65 microns), and K_s (2.17 microns). The positions
are good to about 70 mas, but do not have proper motions associated
with them.
VI. CATALOGS FORTHCOMING
The following is a short list of catalogs that should be available in the near future. Only educated guesses regarding the numbers of stars and accuracies can be made at this time.
UCAC3 Final (USNO CCD Astrograph Catalog):
Expected availability: 2009
The UCAC final will be the culmination of the UCAC project, described above.
It is expected that 80 million stars from V 7.5 to 16.5 covering the entire
sky will be included. Errors in positions will be magnitude dependent
and range from
about 15 to 70 mas. Proper motion errors will be in the 1 to 5 mas/yr range.
VII. DOUBLE STAR CATALOGS
WDS (Washington Double Star Catalog):
Status: Recommended for use
The Washington Double Star Catalog maintained by the USNO is the
official database of double and multiple star data for the International
Astronomical Union. The WDS Catalog contains positions (ICRS),
discoverer designations, epochs, position angles, separations,
magnitudes, spectral types, proper motions, and, when available,
Durchmusterung numbers and Notes for the components of 100,000 systems
based on 650,000 means. The present WDS is a major revision of the
1984.0 and 1996.0 versions. More precise Hipparcos and Tycho magnitudes
have been included where available, as have MK spectral types. A major
observing effort at the USNO has increased the number of systems with
accurate interferometric data, and has also reexamined many unconfirmed
or long-neglected systems. Additionally, observations from Hipparcos
and Tycho are included. The WDS Notes have been extensively revised
to include information on orbital motion and multiplicity (including
astrometric, photometric, and spectroscopic), variability, composite
spectra, etc. Stars with Durchmusterung numbers have been
individually compared with the SIMBAD database. Since new data are
continually being added to the database, the WDS is updated on a nightly
basis. Upon request, data from the catalog are supplied to users
world-wide.
6th Orbit Catalog:
Status: Recommended for use
The data available here include all published orbital elements for
systems whose orbits have been determined. Also included are ephemerides that
span the next five years. The catalog is continually maintained on the
World Wide Web. All orbits are graded on a numerical scale; plots of
each orbit with all available astrometric data also allow the user to
judge a given orbit's quality. Where sufficient measurements have been
made, orbits have been determined for those stars that show orbital
motion. These orbital determinations are periodically published in
leading astronomical journals. In addition, special requests for
ephemerides of orbit stars can be met by the USNO.
VIII. MAGNITUDES AND SPECTRAL TYPES
HD (Henry Draper Catalog):
The Henry Draper Catalogue with 225,300 entries was completed in
1924 and for many years has been the standard source for magnitudes
and spectral types. However, more recent photometric data and
spectral classification (which now often includes luminosity class)
are available for many stars. This is especially true for stars
brighter than 8th magnitude. Hipparcos and Tycho-2 provide 2-color
photometry for most of their stars, which may be sufficient for many
users. However, the best spectral classifications are not
collected into a single source and are, therefore, not conveniently
obtained. The star catalogs listed above give magnitudes, and some
give spectral types though many of these data originally come from the
HD.
IX. PARALLAXES
Hipparcos Catalog:
Status: Recommended for use
One of the primary goals of the Hipparcos mission was to measure accurate
parallaxes for the stars it observed. The mission was successful, and
the Hipparcos parallaxes are among the most accurate found.
See above description for the catalog.
General Catalogue of Trigonometric Stellar Parallaxes, 4th Edition:
Status: Recommended for non-Hipparcos stars
The General Catalogue of Trigonometric Stellar Parallaxes has been
prepared at the Yale University Observatory. This completely revised and
enlarged two-volume edition contains 15,994 parallaxes for 8,112 stars
published before the end of 1995. In this Fourth Edition, 1,722
(27%) new stars have been added to those contained in the previous edition
by Jenkins (1963). The mode of the parallax accuracy for the newly added
stars (0.004" s.e .) is considerably better than in the previous editions
(about 0.016"). Approximately half of the newly added stars are fainter
than the Hipparcos Astrometric Satellite's magnitude limit of 13.0.
Copies of the Catalogue are available from the Yale University
Observatory.
X. VARIABLE STARS
Hipparcos and Tycho-2 Catalogs:
Status: Recommended for use
Both Hipparcos and Tycho-2 include photometry. These are among the best
available and can be utilized. However, the mission lasted only a few
years, so long-term and irregular variables require special attention.
See General Catalog of Variable Stars below.
General Catalog of Variable Stars:
Status: Recommended for long-period and irregular variables, and
non-Hipparcos, non-Tycho-2 stars
The GCVS was the long time standard source for these objects. However,
the Hipparcos photometry superseded the accuracies that can easily be
attained from the ground. However, since Hipparcos was only operational
for three years, the data on the long-period and irregular variables found
in the GCVS may prove more reliable.
The GCVS gives star identifications and rough coordinates as well as maximum
and minimum magnitudes for most stars listed. A period and epoch are given in
some cases, but many of these values are derived from old sources and cannot be
reliably extrapolated to the present. For currently accurate data a literature
search is generally required. The notes section lists other data such
as B-V colors for various parts of the light curve where these
quantities have been determined.
